Methods have been developed using gas chromatography/mass spectrometry (GC/MS) which permits the simultaneous assay in brain and urine samples of phenylethylene glycol, m- & p-hydroxyphenylethanol (mHPE & pHPE), metabolites of phenylethanolamine, m- & p-tyramine, octopamine and dopamine (DA), respectively and 3-methoxy-4-hydroxy phenylethylene glycol (MHPG) and 3,4-dihydroxyphenylglycol, DHPG, both metabolites of norepinephrine (NE). The neutral metabolites are extracted from biological samples by solvent extraction, and the extracts are reacted with pentafluoropropionic anhydride to form volatile derivatives which are analyzed by selected ion monitoring using GC/MS in the chemical ionization made with methane as the reagent gas. Using these methods were have investigated the effects of L-DOPA on the concentrations of the neutral alcoholic metabolites in the brain and urine. L-DOPA (150 mg/kg i.p.) was found to produce a large increase (2-3 fold) in the excretion of DHPG but only a small increase in the excretion of MHPG. The excretion of mHPE and MHPE were increased 8-fold and 23-fold, respectively. L-DOPA produced a large increase in the concentrations of both MHPG and DHPG in rat brain. These results suggest that L-DOPA is significantly converted to NE, but the possible role of NE in behavioral effects produced by L-DOPA are not yet clear.